This invention relates to a fluid signal square root extractor and particularly to such an extractor operable to extract the square root of a flow-related pressure signal for producing an output pressure signal which is a linearized characteristic of pressure versus flow rate.
Various pneumatic and other fluid flow systems develop signals which are the square of the measured quantity or condition. For example, in the heating ventilating and air conditioning art, variable air volume systems are finding wider usage in the control of the environmental air for enclosed spaces. In such systems, outside air and recirculated air are selectively mixed, conditioned and exhausted to maintain room temperature. The control responds to demand changes by varying of the air volume and maintaining the necessary temperature condition. The controls for such systems often are based on sensing the air velocity in the supply and/or exhaust ducts. Conventional velocity pressure sensors and transmittors such as pilot tubes are widely used. Such sensors generate a differential pressure signal which is the square function of the air velocity. Pneumatic differential pressure transmittors generally have a highly linear output over the transmitter span, and thus transmit the nonlinear velocity pressure signal versus velocity. The necessary summing, comparing and similar processing such non-linear pressure signals is difficult because of the nonlinear relationship. Therefore, it is desirable to linearize the velocity scale such that direct and simple signal processing of the velocity related signals with other signals is possible. Although various square root extractors have been suggested, the devices have normally relied on mechanical systems requiring careful processing and quality control, and are generally relatively expensive. There is therefore a need for a simple, reliable and relatively inexpensive square root extractor for processing of fluid signals such as pneumatic signals encountered in heating, ventilating and air control conditioning equipment, as well as other fluid control systems.